The invention relates to active acoustic control systems.
The invention arose during continuing development efforts relating to the subject matter shown and described in U.S. Pat. Nos. 4,677,676, 4,677,677, 4,736,431, 4,815,139, 4,837,834, 4,987,598, 5,022,082, 5,033,082, 5,172,416, and allowed U.S. application Ser. Nos. 07/691,557, 07/794,115, 07/835,721, all incorporated herein by reference. These patents and applications relate to active acoustic attenuation systems. Active acoustic attenuation for sound or vibration cancellation or reduction involves injecting a canceling acoustic wave to destructively interfere with and cancel or reduce an input acoustic wave. In an active acoustic attenuation system the output acoustic wave is sensed with an error transducer such as a microphone or accelerometer which supplies an error signal to an adaptive filter model which in turn supplies a correction signal to a canceling transducer such as a loudspeaker or shaker which injects an acoustic wave to destructively interfere with and cancel or reduce the input acoustic wave.
The present invention provides an active model modeling an actual desired response characteristic, and providing a controlled acoustic path matching same. A model reference is provided having a selectably programmable response. For example, in a vibration control system providing force and/or motion isolation, a certain damping response characteristic may be desired such as over-damped, under-damped, quick response, slow stable response with no overshoot, etc. A model reference is selected or programmed to have such response. An active model is then provided, including in combination an acoustic path and an adaptive filter such that the combination of the acoustic path and the adaptive filter adaptively models the model reference such that the combined response of the acoustic path and the adaptive filter provide an active model response matching the response of the model reference. The acoustic path is a sound duct, a vibration table, a frame, cab, seats, engine or interior of a vehicle, or other complex structures or environments for sound or vibration propagation where it is desired to provide a selectably programmable response of an acoustic wave propagating along an acoustic path to provide a controlled response.
In a further embodiment, the invention additionally provides active acoustic attenuation. A controlled adaptive response to the input acoustic wave is provided, matching the response of the selectably programmable model reference, and additionally the input acoustic wave is attenuated or canceled. The noted adaptively controlled response characteristic facilitates the attenuation because of the noted matching to a known model reference.